The present invention relates to a manufacturing method of olefin polymer wherein the polymerization is conducted at a reaction temperature lower than the melting point of polymer in the presence of a novel catalyst system. In particular, the invention relates to a manufacturing method suitable for obtaining the olefin polymer having a weight average molecular weight of not less than 10,000 by the multistage polymerization method.
It has already been known to use the catalyst system comprising transition metal compound and organometallic compound for the low-pressure polymerization of olefins.
Recently, as a high-activity type catalyst, the catalyst system involving the reaction product of inorganic or organic magnesium compound with transition metal compound as an ingredient is used in many cases.
For example, in U.K. Specification No. 1,464,451 and U.S. Pat. No. 3,901,863, polymerization methods capable of manufacturing polyolefins having an extremely high impact resistance were disclosed, wherein the catalyst systems with an extremely high activity comprising catalyst ingredient (A) obtained by allowing magnesium metal and hydroxylated organic compounds or oxygen-containing organic compounds of magnesium etc., oxygen-containing organic compounds of transition metals and aluminum halide to react and catalyst ingredient (B) of organometallic compounds were used.
Moreover, so-called multistage polymerization system is also known publicly, wherein ethylene is polymerized through a plurality of polymerization processes different in the reaction conditions in the presence of these catalyst systems to control the molecular weight distribution within a wide range. Such polymerization methods are further classified roughly into a method conducting at a reaction temperature higher than the melting point of polymer and that conducting at a reaction temperature lower than the melting point.
The former method necessitates a large quantity of energy for heating etc. since the polymerization is conducted, for example, at 120.degree. to 250.degree. C. Moreover, since there is a restriction of solution viscosity to obtain homogeneous polymer, it has a disadvantageous point industrially that the productivity is low.
Whereas, the latter method does not cause the shortcoming aforementioned since the polymerization is conducted at a temperature lower than the melting point, but the method uses hydrogen ordinarily as a molecular weight modifier and a large quantity of hydrogen is necessary particularly in the polymerization process manufacturing polymer component of low molecular weight by the multistage polymerization method. At this time, there is an inconvenience with these Ziegler type catalyst systems having a high activity, since a reaction that a part of olefin is hydrogenated by hydrogen and paraffins such as ethane, propane, etc., which are disadvantageous industrially, are formed secondarily occurs to an extent impossible to neglect. As a result of this, there occur shortcomings that the yield of polymer per raw material olefin is lowered and the productivity becomes poor.
On the other hand, in the field of ethylene wax, Japanese Unexamined Patent Publication No. 164206/1980 disclosed a manufacturing method to obtain ethylene wax with a viscosity average molecular weight of less than 4,000 at a reaction temperature higher than about 140.degree. C. using a catalyst comprising specific high activity titanium ingredient, organoaluminum ingredient and halogenous compound ingredient, but, in the manufacturing method to obtain high molecular weight olefin polymer with a weight average molecular weight of more than 10,000 at a reaction temperature lower than the melting point of polymer as in the present invention, any technique to inhibit the secondary formation of paraffin was not established.
Furthermore, by the method conducting the polymerization at a temperature lower than the melting point of polymer, the polymer is obtained ordinarily in a state of particles. For this reason, it is extremely important industrially that not only the catalyst system used has a high activity but also the particle properties of the polymer obtained are excellent in order to insure higher productivity.
However, the polymer particles obtainable in the presence of the catalysts disclosed in U.S. Pat. No. 3,901,863 etc. aforementioned were still insufficient in a point of powder characteristics, since a high ratio of fine particles were contained in the polymer particles due to smaller average diameter of particles or wider distribution of particle size.
Namely, when manufacturing the polyolefin, if the polymer particles have a particle size distribution as described above, various difficulties may be caused in the processes such as polymerization, particle separation from the polymer slurry, drying of the powder, transference of the powder, etc., and, in some cases, the continuous production over a long period of time may become impossible. Moreover, when polymer is made by the multistage polymerization method, if the particle size distribution of the polymer particles is wide, the classification of the powder is apt to occur at the formulation stage of the additives and the transportation stage after the drying process and, as the case may be, the polymer with stable quality cannot be obtained since the physical properties are different for every particle diameter.
In addition, the polymer obtainable with these catalyst systems was still insufficient in the molding properties. For example, at the time of the film molding, the wrinkles and slacks are formed on the film product since the melt extruded from die becomes unstable in the process of the solidification and, at the time of the blow molding, the peeling operation of needless portions from molded products, which is called flash separation, is not easy, the strength of molded articles is short because of the thinning of thickness at the pinch-off portion or the like, resulting in the insufficiency of the molding properties and the quality of products.
The method to conduct the polymerization at a reaction temperature lower than the melting point of polymer causes the shortcomings that the yield of polymer per raw material olefin is lowered and the productivity becomes poor as a result of the secondary formation of a large quantity of paraffin disadvantageous industrially at the time of ordinary polymerization, in particular, multistage polymerization, and, at the same time, the loss of raw materials such as ethylene etc. is unavoidable since the needless paraffin formed secondarily accumulates in the polymerization system and this is discharged to outside of the system.
In view of the situation, the inventors have continued the investigation diligently aiming at the provision of a polymerization method of olefins such that the catalyst has a high activity, the molding properties of polymer are excellent and the secondary formation of paraffin is inhibited.
As a result, a manufacturing method of olefin polymer has been found by the combination of specific catalyst ingredients, wherein the catalyst has a high activity, the secondary formation of industrially disadvantageous ethane is prevented and the polymer has a weight average molecular weight of not less than 10,000 and is excellent in the molding properties.